Potential options for wastewater management

The construction of the wastewater treatment plant in 2010 was the first step in improving water quality in the bay.

A condition of the resource consent requires Council to investigate further treatment options to include alternative use and disposal options with the possibility of abandoning the marine outfall pipe altogether. As a minimum, we would have to undertake further treatment which includes making the water clearer and disinfecting it by UV treatment.

The options relate only to the effects of treated wastewater flowing out of the marine outfall pipe. It doesn't deal with other city issues, like wastewater overflows into waterways - see the DrainWise project.

Where to from here

Results from the November 2017 survey indicated a high level of response with some 1183 responses. This high response provides a good level of confidence in the survey results.

The responses showed a clear preference for a high level of wastewater treatment (Options 3, 4 and 5) with a preference for Option 5, which involves the addition of ultra-violet light disinfection, clarification, a 12 ha wetland, wood chip filters, and an additional biological trickling filter to the current WWTP to improve treatment and exceed resource consent water quality requirements.

The identified reasons for selecting these options were primarily community health and the use of the Bay for swimming, and surfing - although shellfish collecting, cultural and personal values alongside affordability/cost were also rated highly in general. This confirms the significant value placed on the Bay for recreation, and the cultural and community connection with it.

Option 1 : Water quality - very good

Makes the water clear and kills most of the ‘bad bugs’ with ultraviolet light. Cost - average annual cost $250, or about $21 a month per household.Benefits - It would meet all water quality standards in the consent.Water Quality - Very Good. All consent water quality parameters met. It would take our wastewater treatment level from one of the lowest in New Zealand to being on par with most similar wastewater disposal systems in the country at this time.User benefits - wastewater quality would be very good and safe to swim in quite close to the ocean outfall. • The chance that the outfall is bad for shellfish on city beaches would be very low. • The seabed area around the outfall pipe could be impacted, but only very close to the outlet. • The wastewater would still go into the bay. We would still aim to find uses for the treated wastewater to stop that from happening.

The next 4 options all add to this option. They cost more but also have more benefits.

Option 2 : Water quality - high

This is Option 1 plus an extra Biological Trickling Filter for an extra $41 per year.

Cost - average annual cost $291, or about $24 a month per household. Benefits - In addition to the benefits of Option 1 - it would also take our wastewater treatment to a level similar with wastewater disposal systems in the country. • This improves water quality by getting rid of more nutrients, with even less effects on the seabed around the outfall. • It would help with managing risks at the treatment plant. Water Quality - High. The wastewater would still go into the bay, but as with all options that are being considered, we would keep on trying to find ways to stop that from happening.

Option 3 : Water quality - very high

This is Option 1 plus it includes a wetland for an extra $74 per year

Cost - average annual cost $324, or about $27 per month per household.Benefits - In addition to the benefits of Option 1 - this includes a wetland. A wetland may ultimately make it possible to stop wastewater from going out the marine outfall into the bay, if enough uses of treated wastewater and disposal methods are found. • Wetlands are good at taking out ‘harder to kill’ bugs (like some viruses) and emerging contaminants which makes swimming, fishing and shellfish safer. • Options 1 and 2 don’t offer this, although they do offer the potential for some removal of domestic wastewater from the outfall.Water quality - Very High. This would take our wastewater treatment to above average when compared with similar wastewater systems around the country, at this time.

This is the preferred option by the Wastewater Management Committee and Turanganui iwi representatives. This would be completed within 10 years.

Emerging contaminants - are like pharmaceuticals and other harmful substances, that are not necessarily removed by engineered wastewater treatment methods. A lot of these don’t easily die off and can end up in the bodies of sea creatures, with possible future environmental and health risks. Harder to kill bugs - include some viruses, bacteria and other organisms that can also get through a conventional wastewater treatment system.

In terms of stopping treated domestic wastewater going out into the bay, we need to find acceptable ways of putting wastewater somewhere else. Or we need to find uses for this treated wastewater. Good disposal options have not been found and Gisborne industries and agricultural businesses have not yet shown an interest in ‘tapping into’ this water potential supply.

The main advantage of Option 4 and 5 is their better ability of taking out emerging contaminants and ‘harder to kill’ bugs. By making the water more acceptable for water users, more water could potentially be used on land, with less going into the bay.

Option 4 - Water quality extremely high

This is Option 1 plus it includes a wetland and woodchip filters for an extra $92 per year.

Cost - average annual cost $342 or $29 per month per household.Benefits - this adds woodchip filters and a wetland onto Option 1. The woodchip filters take out even more nutrients, emerging contaminants, and ‘bad bugs’.Water Quality- Extremely High. Gisborne would be at the leading edge of wastewater management in the country, as treatment of this type has not been installed to this extent before in NZ.

This option is also endorsed by the Wastewater Management Committee and Turanganui iwi representatives. This would be completed within 10 years.

Option 5 - Water quality exceptionally high

This is Option 1 plus it includes a wetland, woodchip filters and adds another Biological Trickling Filter for an extra $133 per year.

Cost - average annual cost $383 or $32 per month per household.Benefits - compared to Option 4, the key benefit is further nutrient removal, although this is not really required from a water quality perspective. However, it would help with operational aspects at the treatment works and reduce risks.Water Quality- Exceptionally High

This option is also endorsed by the Wastewater Management Committee and Turanganui iwi representatives. This would be completed within 10 years.